[SCCP] Constant propagation through freeze instruction

The freeze instruction has not been handled by SCCPInstVisitor.
This patch adds SCCPInstVisitor::visitFreezeInst(FreezeInst &I)
method to handle freeze instructions.

Differential Revision: https://reviews.llvm.org/D151659

Author: Mikhail Gudim

llvm/lib/Transforms/Utils/SCCPSolver.cpp

@@ -17,6 +17,7 @@
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/ValueLattice.h"
 #include "llvm/Analysis/ValueLatticeUtils.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/InstVisitor.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Debug.h"
@@ -612,6 +613,7 @@ class SCCPInstVisitor : public InstVisitor<SCCPInstVisitor> {
   void visitCastInst(CastInst &I);
   void visitSelectInst(SelectInst &I);
   void visitUnaryOperator(Instruction &I);
+  void visitFreezeInst(FreezeInst &I);
   void visitBinaryOperator(Instruction &I);
   void visitCmpInst(CmpInst &I);
   void visitExtractValueInst(ExtractValueInst &EVI);
@@ -1404,6 +1406,25 @@ void SCCPInstVisitor::visitUnaryOperator(Instruction &I) {
   markOverdefined(&I);
 }
 
+void SCCPInstVisitor::visitFreezeInst(FreezeInst &I) {
+  ValueLatticeElement V0State = getValueState(I.getOperand(0));
+  ValueLatticeElement &IV = ValueState[&I];
+  // resolvedUndefsIn might mark I as overdefined. Bail out, even if we would
+  // discover a concrete value later.
+  if (SCCPSolver::isOverdefined(IV))
+    return (void)markOverdefined(&I);
+
+  // If something is unknown/undef, wait for it to resolve.
+  if (V0State.isUnknownOrUndef())
+    return;
+
+  if (SCCPSolver::isConstant(V0State) &&
+      isGuaranteedNotToBeUndefOrPoison(getConstant(V0State)))
+    return (void)markConstant(IV, &I, getConstant(V0State));
+
+  markOverdefined(&I);
+}
+
 // Handle Binary Operators.
 void SCCPInstVisitor::visitBinaryOperator(Instruction &I) {
   ValueLatticeElement V1State = getValueState(I.getOperand(0));

llvm/test/Transforms/SCCP/freeze.ll

@@ -1,6 +1,7 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -passes=ipsccp -S %s | FileCheck %s
 
+@g = global i64 0
 declare void @use(i1)
 
 define i1 @freeze_undef_i1() {
@@ -39,6 +40,48 @@ define <2 x i32> @freeze_undef_vector() {
   ret <2 x i32> %fr
 }
 
+define i1 @freeze_const_i1() {
+; CHECK-LABEL: @freeze_const_i1(
+; CHECK-NEXT:    ret i1 true
+;
+  %fr = freeze i1 1
+  ret i1 %fr
+}
+
+define ptr @freeze_const_ptr() {
+; CHECK-LABEL: @freeze_const_ptr(
+; CHECK-NEXT:    ret ptr inttoptr (i32 256 to ptr)
+;
+  %fr = freeze ptr inttoptr (i32 256 to ptr)
+  ret ptr %fr
+}
+
+define float @freeze_const_float() {
+; CHECK-LABEL: @freeze_const_float(
+; CHECK-NEXT:    ret float 2.500000e-01
+;
+  %fr = freeze float 2.500000e-01
+  ret float %fr
+}
+
+define <2 x i32> @freeze_const_vector() {
+; CHECK-LABEL: @freeze_const_vector(
+; CHECK-NEXT:    ret <2 x i32> <i32 1, i32 2>
+;
+  %fr = freeze <2 x i32> <i32 1, i32 2>
+  ret <2 x i32> %fr
+}
+
+; make sure we don't constant-propagate values that could potentially be poison
+define i64 @maybe_poison() {
+; CHECK-LABEL: @maybe_poison(
+; CHECK-NEXT:    [[FR:%.*]] = freeze i64 add nuw (i64 ptrtoint (ptr @g to i64), i64 123)
+; CHECK-NEXT:    ret i64 [[FR]]
+;
+  %fr = freeze i64 add nuw (i64 ptrtoint (ptr @g to i64), i64 123)
+  ret i64 %fr
+}
+
 define i1 @propagate_range_from_and_through_freeze(i32 %x, i32 %y) {
 ; CHECK-LABEL: @propagate_range_from_and_through_freeze(
 ; CHECK-NEXT:    [[AND:%.*]] = and i32 [[X:%.*]], 3